Blast Hole Plugging Apparatus

ABSTRACT

Apparatus for plugging a hole, such as a bore hole used in blasting, comprises a platform shaped to fit within the hole and to support material such as explosives or stemming at a desired depth in the hole. The platform takes the form of a plate or tray which is generally ellipsoidal in shape so that it fits snugly within the hole when inclined transversely relative to a longitudinal axis of the hole. The plate has a central load support region and a peripheral region for engaging the wall of the hole. The apparatus includes a locking member, typically a length of rigid pipe, attached movably to the platform. The locking member is moveable between a first position in which it is supported clear of the wall of the hole below the platform, and a second position in which it spans the hole to lock the platform in position in the hole. An elongated actuating member in the form of a cord or line is connected to the locking member and platform for lowering the apparatus into the hole and for moving the locking member between its first and second positions.

BACKGROUND OF THE INVENTION

THIS invention relates to apparatus for plugging a hole.

In blasting operations, for example in mining applications, explosive charges are inserted into boreholes drilled into rock or other material to be mined. It is important to locate the explosive charges at the correct depths in the boreholes. In many cases, use is made of stemming material which is held in place over the explosive charges at a suitable height, to modify the effect of the explosives as required.

It is an object of the invention to provide apparatus which can be used to support explosives, stemming or other material in a borehole and which can be located at a desired depth in such a hole.

SUMMARY OF THE INVENTION

According to the invention there is provided apparatus for plugging a hole, the apparatus comprising:

-   -   a platform shaped to fit within the hole and to support material         at a desired depth in the hole, the platform defining a central         load support region and a peripheral region for engaging the         wall of the hole;     -   a locking member attached movably to the platform and moveable         between a first position in which it is supported clear of the         wall of the hole below the platform, and a second position in         which it spans the hole to lock the platform in position in the         hole; and     -   an elongated actuating member connected to the locking member         and platform for lowering the apparatus into the hole and for         moving the locking member between the first and second positions         thereof.

The platform may take the form of a plate or tray which is generally ellipsoidal in shape so that it fits snugly within the hole when inclined transversely relative to a longitudinal axis of the hole.

The central load support region of the platform may be formed with one or more strengthening ribs or ridges.

Preferably, the strengthening ribs or ridges extend parallel to a major axis of the platform.

The strengthening ribs or ridges may define a cavity in an undersurface of the platform in which the locking member can be received in a storage configuration of the apparatus.

At least one transversely extending reinforcing rib may be provided in the cavity to resist flexing of the platform in use.

The peripheral region of the platform is preferably an upstanding wall or skirt that extends substantially parallel to the wall of the hole when the apparatus is seated in the hole.

The locking member is preferably mounted pivotably to an end of the platform.

For example, the locking member may be formed with a pair of opposed apertures which receive respective opposed pins formed in an opening at one end of the platform, so that the locking member can pivot relative to the platform.

In a preferred embodiment, the locking member comprises a length of rigid pipe.

The apparatus may include an end cap which engages an outermost end of the locking member and which defines at least one outwardly extending gripping formation arranged to engage the wall of the hole when the locking member is moved into the second position thereof.

In one embodiment, the gripping formation comprises at least one tooth which can deflect transversely relative to a longitudinal axis of the locking member when the locking member is moved into the second position thereof and the end cap engages the wall of the hole.

The elongate actuating member may be a length of flexible cord or line and is preferably connected to an end of the locking member remote from the platform.

In one embodiment, the cord or line passes through an aperture in the platform, and is preferably secured to the platform by means of a releasable retaining member, with a predetermined length of line between the platform and the end of the locking member.

For example, the line may be attached to the platform by means of a frangible tab, which breaks or releases when the line is pulled sharply to allow the end of the locking member to move upwardly relative to the platform, to lock the apparatus in the hole.

In another embodiment, a pair of apertures of different sizes are defined in the platform, interconnected by a slot, to allow an enlarged part of the cord or line to be moved from a position in which it is retained against a first, smaller aperture, via the slot and through a second, larger aperture when the cord or line is pulled sharply, to permit the cord or line to move the locking member upwardly relative to the platform, to lock the apparatus in the hole.

The platform may be formed from polypropylene, polyethylene, glass fibre and resin, or sheet metal, for example.

The locking member comprises PVC or ABS pipe, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial view of a first embodiment of apparatus for plugging a hole according to the invention;

FIGS. 2, 3 & 4 are schematic side views showing the apparatus of FIG. 1 in a borehole, in use;

FIG. 5 is a pictorial view of the underside of a second embodiment of apparatus according to the invention;

FIG. 6 is a pictorial view of a gripping member forming part of the apparatus of FIG. 5;

FIG. 7 is a schematic side view showing the apparatus of FIGS. 5 and 6 in a borehole in use; and

FIG. 8 is a partial sectional side view showing the operation of the gripping member of FIG. 6 in use.

DESCRIPTION OF EMBODIMENTS

FIG. 1 shows an embodiment of apparatus for plugging a hole comprising a platform 10 and a locking member 12. The platform 10 is moulded from a tough plastics material such as polypropylene and comprises a generally planar central region 14 with an upstanding peripheral skirt or wall 16. Although polypropylene is preferred, the platform can be manufactured from other materials, including other plastics such as polyethylene or PVC, glass fibre and resin, or even sheet metal such as stamped aluminium sheet.

The central region 14 is designed to carry a load of material, which could be explosives or stemming material in a typical application. The central region is generally elliptical or ellipsoidal in shape and includes a large stiffening rib or ridge 18 which is aligned with the longitudinal axis of the elliptical region. The upstanding side wall or skirt 16 is generally cylindrical in shape, with the axis of the cylinder being inclined at approximately 45° relative to the plane of the load support platform 14. The height of the wall 16 is at a maximum at a first point 20 and at a minimum at closely spaced opposed points 22 and 24, at opposite ends of the long axis of the elliptical load support region 14.

Between the adjacent peripheral wall end portions 22 and 24 is an opening in which one end 26 of the locking member 12 is received. Typically, the locking member comprises a length of rigid PVC pipe. Other suitably strong and rigid materials such as ABS are also suitable. The end 26 of the locking member is cut at an angle of approximately 70° relative to the axis of the pipe, while the other end 28 is cut at 90°.

A pair of opposed apertures are formed in the end 26 of the locking member which receive respective pins (not shown) formed in the wall end portions 22 and 24 to mount the locking member pivotably on the platform. The free end 28 of the locking member hangs below the platform in use, with one end 30 of a line or cord 32 secured to it. The line or cord 32 passes through an aperture 34 in a tapered end portion of the stiffening rib 18, and is secured to a trigger device comprising a frangible breakaway tab (not shown) so that the entire apparatus can be raised or lowered at the end of the cord or line 32, with the position of the lower end 28 of the locking member being determined by the length of a portion 36 of the line between the locking member and the underside of the platform.

In this configuration, as shown in FIG. 2, the apparatus can be lowered into a borehole 38, with the underside of the platform and the locking member defining an oblique angle between one another, or preferably an angle of 180°, so that the apparatus does not snag the wall 40 of the borehole.

When the apparatus is at the correct depth in the borehole, a sharp upward jerk on the cord or line 32 breaks the frangible tab, allowing the line to pass freely through the aperture in the platform. This allows the lower end 28 of the locking member to swing upwardly as illustrated in FIG. 3, while the tapered shape of the platform allows it to come to rest in the borehole in the position shown in FIG. 3. This locks or wedges the platform and the locking member in position in the borehole, and positions the platform above the locking point at an angle of about 45° relative to the axis of the borehole. It is important that the platform be at an angle to ensure that the load is on the locking point and not on the opposite side, as that would cause the locking member to dislodge and the load to slip downward in use.

If stemming, explosives or other material are now placed on the platform while upward pressure is maintained on the cord or line 32, the force exerted by the material tends to increase the wedging force on the platform and the locking member, holding the platform securely in position in the borehole and allowing a substantial load to be carried by the platform in use. Once the apparatus is wedged in place, the cord or line 32 is no longer needed. By contrast, other known apparatus that can support a load of explosives or stemming on a platform requires the support of a cord tied to a brace at the top of the bore hole.

The described apparatus is simple and inexpensive to manufacture, but effective in use. Unlike apparatus having an inflatable body which wedges itself in the borehole when sufficiently inflated, the described apparatus can be used in water-filled holes, making it relatively versatile.

In operation, the load on the platform of the apparatus is transferred to the lowest point thereof, where the platform connects pivotably to the locking member. This is achieved by arranging the platform at an angle relative to the axis of the blast hole. This arrangement causes stemming supported by the platform to be tapered in a wedge shape, which enhances the effect of the stemming in use.

FIGS. 5, 6 and 7 illustrate an alternative embodiment of the apparatus. Once again, the device comprises a platform 100 and an associated locking member 102, which can be formed of the same materials as described above. The platform has a relatively large upstanding stiffening rib or ridge 104 which extends above the planar load bearing portion 106 of the platform and is aligned with the longitudinal axis of the platform. From the underside, as illustrated, the rib defines a half-cylindrical cavity 108 in which the locking member can be received in a storage configuration of the device.

Located between the midpoint of the cavity 108 and the point of attachment of the locking member are several stiffening ribs 110 which extend transversely across the cavity. The ribs have a crescent shaped profile which, together with the depth of the cavity, provides sufficient clearance for approximately half the volume of the locking member to be received within the cavity. The ribs help to stiffen the platform 106 against transverse flexing in use, particularly in the operatively lowermost region thereof which is subject to the greatest load. Upstanding side wall or skirt portions 138 and 140 have a gap or opening 142 between them at one end of the platform and a cut-out (see below) at the other end of the platform, enabling the side wall portions to flex somewhat in use relative to the central load-bearing portion of the apparatus, to accommodate irregularities in the shape of a borehole in which the apparatus is used.

A pair of mushroom headed pins 112 and 114 are formed facing one another at either side of a cut-out 116 which accommodates the end of the locking member 102. As described above, the locking member is provided with a pair of opposed holes which receive the pins 112 and 114, retaining the locking member in position firmly but pivotably at one end of the platform.

At the opposite end of the cavity 108 is an inclined surface 118 in which is defined a trigger formation 120 comprising a pair of holes joined by a narrow slot. The innermost hole of the two is somewhat smaller in diameter than the outermost hole and prevents passage of a knot 122 in a cord 124 secured to the locking member 102 at or near its outermost end. However, when the apparatus is lowered into a borehole in the same manner as the embodiment of FIGS. 1 to 4, a sharp jerk on the cord from above causes the knot 122 to slide against the under surface of the platform and the cord to slip through the slot into the larger hole, through which the knot 122 can pass, thus triggering the apparatus as described above.

Referring to FIG. 6, an end cap 126 is shown which is designed to fit over the outermost end of the locking member 102 and which defines gripping formations which engage the wall 128 of the borehole in use. The end cap 126 can be moulded from polypropylene or other materials including polyethylene, nylon, ABS, polystyrene or PVC, and has a tubular body 130 which is sized to fit tightly over the length of pipe or tubing defining the locking member 102. An inclined face 132 is formed at one end of the body 130 defining an upstanding partial peripheral ridge 136 and several axially outwardly extending projections or teeth 134. The projections 134 are stiff but somewhat flexible and have a length of approximately 6 to 12 mm, typically 8 to 10 mm, enabling them to bend slightly when subjected to a transverse force. Thus, when the locking member 102 is subjected to a transverse force in the direction of the arrow A in FIGS. 7 and 8 due to an upward force applied via the cord 124, the outer ends of the projections 134 drag against the inner surface 128 of the borehole, pulling them slightly out of alignment with the longitudinal axis of the locking member 126 as shown in FIG. 8. This causes the projections or teeth to dig into the surface 128 and resist dislodgment of the locking member in use, as the locking member is brought into engagement with the inner surface of the borehole. Once the locking member is fully engaged, the ridge 136 of the end cap 126 is forced into tight engagement with the surface of the borehole.

The described apparatus has been tested successfully with loads of up to 700 kg, and is relatively inexpensive to manufacture, simple to deploy and reliable in use. 

1. Apparatus for plugging a hole, the apparatus comprising: a platform shaped to fit within the hole and to support material at a desired depth in the hole, the platform defining a central load support region and a peripheral region for engaging the wall of the hole; the peripheral region including an upstanding wall or skirt that extends substantially parallel to the wall of the hole when the apparatus is seated in the hole; a locking member attached movably to the platform and moveable between a first position in which it is supported clear of the wall of the hole below the platform, and a second position in which it spans the hole to lock the platform in position in the hole; and an elongate actuating member connected to the locking member and platform for lowering the apparatus into the hole and for moving the locking member between the first and second positions thereof.
 2. The apparatus of claim 1 wherein the platform comprises a tray which is generally ellipsoidal in shape so that it fits snugly within the hole when inclined transversely relative to a longitudinal axis of the hole.
 3. The apparatus of claim 1 wherein the central load support region of the platform is formed with at least one strengthening rib or ridge.
 4. The apparatus of claim 3 wherein said at least one strengthening rib or ridge extends parallel to a major axis of the platform.
 5. The apparatus of claim 4 wherein said at least one strengthening rib or ridge defines a cavity in an undersurface of the platform in which the locking member can be received in a storage configuration of the apparatus.
 6. The apparatus of claim 5 wherein at least one transversely extending reinforcing rib is provided in the cavity to resist flexing of the platform in use.
 7. The apparatus of claim 1 wherein the locking member is mounted pivotably to an end of the platform.
 8. The apparatus of claim 7 wherein the locking member is formed with a pair of opposed apertures which receive respective opposed pins formed in an opening at one end of the platform, so that the locking member can pivot relative to the platform.
 9. The apparatus of claim 7 wherein the locking member comprises a length of rigid pipe.
 10. The apparatus of claim 9 including an end cap which engages an outermost end of the locking member and which defines at least one outwardly extending gripping formation arranged to engage the wall of the hole when the locking member is moved into the second position thereof.
 11. The apparatus of claim 10 wherein said at least one gripping formation comprises at least one tooth which can deflect transversely relative to a longitudinal axis of the locking member when the locking member is moved into the second position thereof and the end cap engages the wall of the hole.
 12. The apparatus of claim 1 wherein the elongate actuating member is a length of flexible cord or line connected to an end of the locking member remote from the platform.
 13. The apparatus of claim 12 wherein the cord or line passes through an aperture in the platform, and is secured releasably to the platform, with a predetermined length of cord or line between the platform and the end of the locking member.
 14. The apparatus of claim 13 wherein the cord or line is attached to the platform by means of a frangible tab, which breaks or releases when the cord or line is pulled sharply to allow the end of the locking member to move upwardly relative to the platform, to lock the apparatus in the hole.
 15. The apparatus of claim 13 wherein a pair of apertures of different sizes are defined in the platform, interconnected by a slot, to allow an enlarged part of the cord or line to be moved from a position in which it is retained against a first, smaller aperture, via the slot and through a second, larger aperture when the cord or line is pulled sharply, to permit the cord or line to move the locking member upwardly relative to the platform, to lock the apparatus in the hole.
 16. The apparatus of claim 1 wherein the platform is formed from polypropylene, polyethylene, glass fibre and resin, or sheet metal.
 17. The apparatus of claim 1 wherein the locking member comprises PVC or ABS pipe.
 18. (canceled) 